Gas-phase oxydehydrogenation of ethylbenzene with nitrobenzene by hydrogentransfer catalyzed reaction to produce styrene and aniline

Gas-phase catalytic hydrogen transfer reaction between ethylbenzene and nit robenzene, to produce styrene and aniline, has been carried out at 360-460 degrees C on amorphous AlPO4, SiO2, Al2O3, and on a natural sepiolite, as w ell as on the corresponding 20 wt% supported nickel catalysts. The influenc e of Cu as a second metal was also studied. Reactions were also carried out without nitrobenzene, under nonoxidative conditions. Catalytic activity un der oxidative conditions was always comparatively higher than in nonoxidati ve conditions. In both cases, styrene yield and selectivity values obtained with support materials directly used as catalysts were better than those o btained with the corresponding Ni or Ni-Cu supported metal catalysts, with the only exception of SiO2. The best results were obtained when amorphous A lPO4 was used as the catalyst. The catalytic activity obtained in both oxid ative and nonoxidative conditions, was closely associated to acid-base prop erties of the catalysts studied. Furthermore, a very similar linear correla tion between ln A and E-a known as "compensation effect" was obtained and a common dehydrogenation mechanism was considered for oxidative and nonoxida tive conditions. However, without considering the catalyst, nitrobenzene pl ays an important role as hydrogen acceptor, not only shifting the ethylbenz ene dehydrogenation equilibrium but also avoiding secondary reactions by lo wering the level of available hydrogen, especially when supported metals ar e being used as catalysts.